Shoe press belt

ABSTRACT

To provide a shoe press belt that is more excellent in the properties such as abrasion resistance, bending fatigue, crack resistance, and compression fatigue resistance. The shoe press belt has polyurethane and a substrate, wherein the polyurethane contains a non-reactive polydimethylsiloxane liquid substance and has a JIS A hardness of 93° to 96°.

This application claims the benefit of U.S. Provisional Application No. 60/637,463, filed Dec. 21, 2004, which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a shoe press belt useful for a paper shoe press, and particularly to a shoe press belt useful for a shoe press of closed type. More particularly, the invention relates to a shoe press belt having the resin layers composed of polyurethane having a specific composition and hardness, and having excellent physical properties of crack resistance, abrasion resistance, and bending fatigue resistance.

2. Description of the Background Art

In a shoe press process, a shoe press mechanism 100 comprising a looped shoe press belt 1 interposed between a press roll 101 and a shoe 102 is employed, a wet paper (not shown) is passed between the press roll 101 and the shoe press belt 1 in a press portion formed by the press roll 101 and the shoe 102 to make dehydration, as shown in FIG. 1.

Also, the shoe press belt 1 has the resin layers 5, 6 integrally provided on both sides of a substrate 3, and many concave grooves 7 are formed on the surface of a resin layer 5 on the press roll side, as shown in a cross-sectional view of FIG. 2. Water squeezed from a wet paper at the time of pressing is held in the concave grooves 7, and further held water is transferred out of the press portion by the rotation of the belt itself. Therefore, it is required that the projections 8 provided on the resin layer 5 on the press roll side serve to improve the mechanical characteristics in terms of abrasion, bending fatigue, crack, and compression fatigue caused by a vertical pressing force of the press roll 101 and a friction or bending fatigue of the belt in a shoe press area.

From these reasons, as the material forming the resin layers 5, 6 of the shoe press belt 1, polyurethane excellent in the crack resistance is broadly employed (e.g., refer to Japanese Patent Unexamined Publication Nos. JP-A-11-247086 and JP-A-2004-52204).

However, in recent years, the service environments of the shoe press belt 1 are increasingly severe as the operation speed or the pressure of the press portion is increased owing to higher productivity of paper. Therefore, it is required that various mechanical characteristics are further improved.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the invention to provide a shoe press belt having the excellent properties such as abrasion resistance, bending fatigue resistance, crack resistance, and compression fatigue resistance. In order to achieve the above object, the present invention provides a shoe press belt comprised of polyurethane and a substrate, characterized in that the polyurethane contains a non-reactive polydimethylsiloxane liquid substance and has a JIS A hardness of 93° to 96°.

Since the shoe press belt of the invention is composed of polyurethane forming the resin layers, which contains non-reactive polydimethylsiloxane and has a JIS A hardness of 93° to 96°, it has more excellent mechanical characteristics such as abrasion resistance, bending fatigue, crack resistance, and compression fatigue resistance than conventionally and is good for service under severe conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a shoe press mechanism;

FIG. 2 is a cross-sectional view showing a shoe press belt;

FIG. 3 is a schematic view showing an apparatus for measuring the occurrence number of cracks; and

FIG. 4 is a schematic view showing an apparatus for measuring the abrasion loss.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described below with reference to the accompanying drawings.

A shoe press belt of the invention is integrally formed with the resin layers 5, 6 on both sides of a substrate 3, and provided with many concave grooves 7 on a resin layer 5 on the side of a roll press, as shown in FIG. 2. The resin layers 5, 6 are formed of polyurethane containing a non-reactive polydimethylsiloxane liquid substance and having a JIS A hardness (hereinafter referred to as a hardness) of 93° to 96°.

Polyurethane containing the non-reactive polydimethylsiloxane liquid substance and having a hardness of 93° to 96° is prepared from urethane prepolymer, a curing agent, and non-reactive polydimethylsiloxane liquid substance by adjusting their mixture ratio to have a hardness of 93° to 96° when cured (hereinafter referred to as a “hardness 93° to 96° product containing non-reactive polydimethylsiloxane liquid substance”). Also, polyurethane not containing non-reactive polydimethylsiloxane liquid substance prepared by adjusting the mixture ratio of urethane prepolymer and curing agent to have a hardness of 98° (hereinafter referred to as a “hardness 98° product not containing non-reactive polydimethylsiloxane liquid substance”), and polyurethane containing non-reactive polydimethylsiloxane liquid substance prepared by adjusting the mixture ratio of urethane prepolymer, curing agent and non-reactive silicone oil liquid substance to have a hardness of 90° to 93° (hereinafter referred to as “hardness 90° to 93° product containing non-reactive polydimethylsiloxane liquid substance”) may be blended.

Urethane prepolymer is prepared by reacting an organic diisocyanate and polyol by a well-known method. Suitable examples of organic diisocyanate include paraphenylene diisocyanate (PPDI), triden diisocyanate (TODI), isophorone diisocyanate (IPDI), 4,4′-methylene bis(phenylisocyanate) (MDI), toluene-2,4-diisocyanate (2,4-TDI), toluene-2,6-diisocyanate (2,6-TDI), naphthalene-1,5-diisocyanate (NDI), diphenyl-4,4′-diisocyanate, dibenzyl-4,4′-diisocyanate, stilbene-4,4′-diisocyanate, benzophenone-4,4′-diisocyanate, 1,3- and 1,4-xylene diisocyanate, 1,6-hexamethylene diisocyanate, 1,3-cyclohexyl diisocyanate, 1,4-cyclohexyl diisocyanate (CHDI), 1,1′-methylene-bis(4-isocyanate hexamethylene), three geometrical isomers (abbreviated collectively as H₁₂MDI) and their mixtures.

High molecular weight polyol having long chain, for example, having a molecular weight (MW) of more than 250, is typically employed to form prepolymer. The high molecular weight polyol having long chain provides the rein flexibility and elastomer property. The high molecular weight polyol, typically polyether polyol, polyester polyol, or hydrocarbon polyol having a number average molecular weight of at least 250, is often employed to prepare prepolymer. The molecular weight is preferably from about 500 to 6000, but more preferably in a range from about 650 to about 3000. However, the high molecular weight polyol has a high molecular weight of about 10,000, and a low molecular weight of about 250. Moreover, the low molecular weight glycol and triol having a molecular weight of 60 to 250 may be contained.

Suitable polyalkyleneetherpolyol is represented by a general formula “HO(RO)_(n)H”, where R is alkylene radical, and n is an integer in which polyether polyol has a number average molecular weight of at least 250. Polyalkylene ether polyol is well-known polyurethane product component and prepared by polymerizing cyclic ether, for example, alkylene oxide, glycol, and dihydroxy ether by a well-known method. The average functional group number is from about 2 to about 8, preferably from about 2 to about 3, or more preferably from about 2 to about 2.5.

Polyester polyol is typically prepared by reacting dibasic acid (usually adipic acid, but other components, for example, glutaric acid, succinic acid, azelaic acid, sebacic acid, or phthalic anhydride may exist) with diol, for example, ethylene glycol, 1,2-propylene glycol, 1,4-butylene glycol, 1,6-hexylene glycol, diethylene glycol, or polytetramethyleneetherglycol). If the chain is branched or ultimately bridged, polyol, for example, glycerol, trimethylolpropane, penthaerythritol, or sorbitol can be employed. Diester may be employed instead of dibasic acid. Some of polyester polyol is produced employing caprolactam, or dimerization unsaturated fatty acid.

Hydrocarbon polyol is prepared from ethylene unsaturated polymer, for example, ethylene, isobutylene, and 1,3-butadiene. For example, polybutadienpolyol is employed, such as “Poly-bd R-45HT” made by Atochem, “DIFOL” made by Amoco Corp., and “Kratone” L polyol” made by Shell Chemical CO.

Polycarbonate polyol is also usable, and prepared by reacting glycol (e.g., 1,6-hexyline glycol) and organic carbonate (e.g., diphenylcarbonate, diethylecarbonate, or ethylenecarbonate).

A curing agent or chain elongation agent for use with prepolymer is selected from various kinds of organic diamine or polyol materials which are usually used and well known. Preferable material is solid or liquid having a low melting point. Particularly, diamine, polyol, and a blend thereof, having a melting point of below 140° C. are preferred. Generally, diamine or polyol is currently employed as the curing agent for polyurethane in this industry. The curing agent is generally selected on the basis of the required reactivity, required property needed in specific uses, required processing conditions, and a desired pot life. A well-known catalyst may be employed in combination with the curing agent.

The curing agent may be aliphatic diol or aromatic diamine. Suitable examples of aliphatic diol include 1,4-butadiendiol, 1,3-propanediol and 1,6-hexanediol. Also, suitable examples of aromatic diamine include dimethyl thio toluene diamine (DMTDA), and 3,3′-dichrolo 4,4′-diaminodiphenylmethane (MBOCA). Among others, DMTDA and MBOCA are preferable. Also, various isomers of DMTDA exist depending on the substitution position of dimethylthio group and amino group, but may be employed in the form of isomer mixture and is available as “(ETHACURE) 300” made by Albemarle Corporation in United States.

The use percentage of urethane prepolymer and the curing agent is adjusted depending on the hardness, but it is preferable that the equivalent ratio of active hydrogen group of curing agent and isocyanate group of urethane prepolymer is from 0.9 to 1.10.

The non-reactive polydimethyl siloxane liquid substance is preferably high molecular compound containing siloxane, such as silicone oil, silicone rubber and silicone elastomer. Those silicones may be commercially available from Wacker Silicones Corporation with a tradename “Silicone Fluids SWS-101”, belonging to the silicone fluids, and “KF96” made by Shinetsu Chemical.

The non-reactive polydimethylsiloxane liquid substance may have any viscosity (used as a criterion of chain length in this specification) as far as it is effective to improve the abrasion resistance of the product without losing the friction characteristic of the product containing it. Accordingly, the viscosity is 200,000 cst or more, and preferably in a range from 5,000 to 100,00 cst.

Also, the non-reactive polydiraethylsiloxane liquid substance is blended at a percentage of 0.5 to 25mass % to the total amount of urethane prepolymer and the curing agent.

The shoe press belt is produced by applying and impregnating a mixture of hardness 93° to 96° product containing non-reactive polydimethylsiloxane liquid substance or hardness 93° product containing non-reactive polydimethylsiloxane liquid substance and hardness 98° product not containing non-reactive polydimethylsiloxane liquid substance onto the substrate, curing the mixture by heating, then polishing the surface to have a predetermined thickness, and forming the concave grooves on one surface in the same manner as conventionally, as shown in FIG. 2. Though the curing conditions are appropriately selected depending on the kind of used product, the heating temperature is from 20 to 150° C., preferably from 90 to 140° C., and the heating time is 30 minutes or longer.

The substrate may be a film or knit, narrow strip made of polyamide, polyester, aromatic polyamide, aromatic polyimide, or high strength polyethylene, and wound like spiral, for example.

EXAMPLES

This invention will be described below by way of example, but is not limited to those examples.

Examples 1 to 8 and Comparative Examples 1 to 12

Employing hardness 93° product containing non-reactive polydimethylsiloxane liquid substance (adiprenestream “E493” made by Uniroyal), hardness 93° product not containing non-reactive polydimethylsiloxane liquid substance (adiprene LF930A made by Uniroyal), and hardness 98° product not containing non-reactive polydimethylsiloxane liquid substance (adiprene LF600D made by Uniroyal), a mixture of them is applied on both the surfaces of a substrate made from polyester fabric, and cured by heating, whereby the concave grooves (0.5 to 4 mm wide, 0.5 to 5 mm deep) are formed with the land part interval between adjacent waterways being 2 to 3 mm on one surface to produce a belt sample. In the comparative examples 1 to 12, polyurethane contains no non-reactive polydimethylsiloxane liquid substance.

And for each belt sample, (1) hardness, (2) occurrence number of cracks, (3) abrasion loss and (4) VV reduction ratio under pressure were measured. A measuring method is as follows, and the results are listed in the table.

(1) Hardness

The hardness was measured employing a JIS A durometer.

(2) Occurrence Number of Cracks

Both ends of a belt sample 51 were pinched by the clamp hands 52, 52, and the clamp hands 52, 52 were linked and reciprocated in the left and right direction in the figure, as shown in FIG. 3. At this time, the tension applied on the belt sample 51 was 3 kg/cm, and the reciprocation speed was 40 cm/sec. Also, the belt sample 51 was carried by a rotary roll 53 and a press shoe 54, and the press shoe 54 was moved in a direction of the rotary roll to pressurize the belt sample 51 with a pressure of 36 kg/cm². A lubricant oil was sprayed from the press shoe side onto the belt sample 51 during the reciprocating movement to suppress generation of heat. The belt sample 51 was reciprocated in this way, whereby the number of reciprocations was measured until a crack occurred on a face of the belt sample 51 opposed to the rotary roll.

(3) Abrasion Loss

Employing an apparatus as shown in FIG. 4, the belt sample 51 was attached on the lower part of a press board 55, and rotated with a rotary roll 56 having a rubber 57 on the outer circumference pressed against a lower face (measurement object face) thereof. At this time, the pressure with the rotary roll 56 was 3 kg/cm, and the rotation rate of the rotary roll 56 was 100 m/min, whereby the belt sample was rotated for ten minutes. After rotation, a decrease amount in the thickness of the belt sample 51 was measured.

(4) VV Reduction Ratio Under Pressure

Two belt samples were prepared, uncured silicone resin (before curing) was filled in the concave grooves of one belt sample, scraped smoothly over the belt grooves by a scoop, and cured without pressure.

Uncured silicone resin (before curing) was filled in the concave grooves of another belt sample, scraped smoothly over the belt grooves by a scoop, and cured under a pressure of 40 kg. After curing, resin was taken out of the concave grooves of each belt sample, and the groove sizes (groove width, groove height, groove length) were measured by a microscope, whereby the VV reduction ratio under pressure was calculated from the following expression. [(VV without pressure−VV under pressure)/VV without pressure]×100%

TABLE 1 Occurrence VV Adiprene Adiprene Adiprene Amine Number of Abra- reduc- E493 LF930A LF950 A LF600D curing Hardness cracks sion tion Total NCO agent Equivalent JIS (10000 loss ratio eval- 5.12 5.07 6.01 7.18 NCO (NH2) NH2/NCO ratio-A times) (mm) (%) uation Comparative 90 0 0 10 5.33 DMTDA 0.95 92 >30 0.25 41 bad example 1 Example 1 70 0 0 30 5.74 DMTDA 0.96 93 20-25 0.35 30 good Example 2 50 0 0 50 6.15 DMTDA 0.98 94 15-20 0.35 23 excel- lent Example 3 40 0 0 60 6.36 DMTDA 1.01 95 10-15 0.45 18 good Example 4 30 0 0 70 6.56 DMTDA 1.03 96  5> 0.60 14 better Comparative 20 0 0 80 6.77 DMTDA 1.05 97  5> 0.65 11 bad example 2 Comparative 90 10 0 0 5.12 MOCA 0.95 92 >30 0.25 43 bad example 3 Example 5 90 0 0 10 5.33 MOCA 0.97 93 20-25 0.25 35 better Example 6 70 0 0 30 5.74 MOCA 0.99 94 15-20 0.25 24 excel- lent Example 7 50 0 0 50 6.15 MOCA 1.01 95  5-10 0.35 19 good Example 8 40 0 0 60 6.36 MOCA 1.03 96  5> 0.50 15 better Comparative 30 0 0 70 6.56 MOCA 1.05 97  5> 0.55 17 bad example 4 Comparative 0 0 100 0 6.01 DMTDA 0.97 94 15-20 0.65 28 bad example 5 Comparative 0 90 0 10 5.28 DMTDA 0.95 92 >30 0.65 40 bad example 6 Comparative 0 70 0 30 5.70 DMTDA 0.96 93 15-20 0.60 30 bad example 7 Comparative 0 50 0 50 6.13 DMTDA 0.98 94  5-10 0.65 23 bad example 8 Comparative 0 0 100 0 6.01 MOCA 0.99 95 10-15 0.70 25 bad example 9 Comparative 0 90 0 10 5.28 MOCA 0.97 93  5-10 0.75 31 bad example 10 Comparative 0 70 0 30 5.70 MOCA 0.99 94  5> 0.70 24 bad example 11 Comparative 0 50 0 50 6.13 MOCA 1.01 95  5> 0.70 18 bad example 12 Target ≧10 0.5≦ 30≦

As seen from the table, the belt sample made of polyurethane containing non-reactive polydimethylsiloxane liquid substance and having a hardness of 93° to 96° was more excellent in the crack resistance and the abrasion resistance and had less deformation in the concave grooves than any other belt sample.

While there has been described in connection with the preferred embodiments of the present invention, it will be obvious to those skilled in the art that various changes and modification may be made therein without departing from the present invention, and it is aimed, therefore, to cover in the appended claim all such changes and modifications as fall within the true spirit and scope of the present invention. 

1. A shoe press belt comprising polyurethane and a substrate, wherein said polyurethane contains a non-reactive polydimethylsiloxane liquid substance and has a JIS A hardness of 93° to 96°.
 2. The shoe press belt according to claim 1, wherein said polyurethane is a mixture of polyurethane having a JISA hardness of 90° to 93° and containing a non-reactive polydiluethylsiloxane liquid substance, and polyurethane having a JIS A hardness of 98° and not containing a non-reactive polydimethylsiloxane liquid substance. 